Signaling system



lMarch 30, 1948.

y H. M. BASCOM ETAL SIGNALING SYSTEM v Fiied Aug. l17, 1944 2sheexssheet .1

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B. OSTENDORF JR.

au. @Ascou /NVEA/rons R. EmssoN/VEAU 17H54 av March 30, 1948. H. M.BAscoM ETAL SIGNALING SYSTEM Filed Aug. 1'7, 1944 2 sheets-sheet 2 u r2' Ess Q Sl - R' 'NVENTORS s'. srENoonF, Jn.

. .y ZREA ATTORNEY Patented Mar. 30, 1948 2.438.492 sionismo srs'rmuHenry M. Bascom, New York, Robert F. Massonnean, Scandale, BernardOstendorf, Jr., Jamaica, and Wilton T. Rea, Manhasset, N. Y., assignorsto Bell Telephone Laboratories, lincorporated, New York, N. Y., acorporation of .1

New York Application August I7, met, Serial No. Miiz Claims. (Cl.itt-380) This invention relates to signaling systems and start-stop"oscillator therein and received in a circuit which responds to bothpositive and negative half cycles, inverts the negative half cycles andcauses both the positive half cycles and the inverted negative halfcycles to be recorded by the tubes oi a counting chain, said tubesconditioning, in succession, the tubes oi a second chain for operatingthe tube therein last conn ditioned subsequent to the reception ci thelast half cycleof the signal train.

Broadly speaking, the present invention repre sents, in a number` ofrespects, an improvement of the signaling system disclosed and claimedin the copending application of R. F. Massonneau, Serial No. 453,843,led August 6, 1942, now U. S. Letters Patent 2,373,134, granted April10, 1945.

The various features of the invention will be understood from thefollowing description when considered in connection with theaccompanying two. sheets of drawings, the scope of the invention beingmore particularly pointed out in the appended claims.

In the accompanying drawings, Fig. 1` shows the transmitter and Fig. 2shows the receiver, said figures being placed adjacent to each otherfrom left to right in the order named to disclose the inventioncompletely.

The transmitter, shown in Fig. 1, comprises a start-stop oscillator ofthe type disclosed in A Patent No. 2,370,685, issued to W. T. Rea. andJ.

R. Wilkerson on March 6, 1945; a counting chain consisting of tencoldcathode gas-filled tubes CTICTD, a recycling circuit comprising two coldcathode gas-rilled tubes GI and G2 by means of which single orrepetitive transmission o f a pulse train is accomplished, a linecoupling circuit comprising a potentiometer network RZB-R29 anda lineamplifying tube L by means of which the oscillator is coupled to theline, the double triode D by means of which it is insured that only thepredetermined number of oscillations are caused to be applied to theline, an impulse control circuit including the transformer IT and theupper triode of tube A by means of which each half cycle applied, to theline is caused to be registered on one of the tubes of the countingchain CTI-CTO, and a restoring circuit including the upper triode oftube B and the vacuum tube C 2 recycling circuit, extinguishes the tubeof the counting chain.

Thelreceiver, shown in Fig. 2, comprises a two stage direct currentampliier employing a double triade tube RL; a detector, inverter andimpulse amplier operating on odd half cycles, all of lwhich comprisethree of the trodes of the double triode tubes DETl, DET2 and INV; a.detector and impulse amplifier operating on even half cycles whichcomprises two triodes of the trlode tubes DETZZ and INV; a recyclingcircuit comprising the twoy triodes of vacuum tube'RE and the vacuumtubes EXT and SEL; a counting chain circuit consisting of ten coldcathode gas-filled tubes C'I'Rl-C'I'Rt; and a marking chain consistingofv the ten coldcathode gas-filled tubes Si-Sit Referring now moreparticularly to Fig. 1, the general operation of the transmitter is asfollows:

During the interval when no signal is being transmitted the oscillatorOC is held in a non oscillating condition and the line coupling circuitis so conditioned as' to prevent any impulses from being applied to theline. At this time, all the tubes GTi-CTD of the counting chain aremaintained in the non-conducting condition. Now when a signal consistingof a certain number of positive andnegative half-cycles of a continu`ous alternating current train is to be transmitted over line LN, aconnection is made between a common conductor and a tube in thelcounting chain CTI-CTU that marks the last half cycle of the' desiredsignal train. At this time the recycling tube G2 becomes energized tocondition the tubes of the counting chain for operation, starts theoscillator OC and removes the block in the line coupling circuit. Thesine wave produced by the oscillator OC -is thus permitted to beimpressed on theline LN. Each time the oscillator completes a half cycleitcauses an impulse generating circuit to .produce an impulse which resone of the tubes of the counting chain, and each tube, as it fires,conditions the succeeding tube to be fired by the following impulse.Thus the tubes of the counting chain are fired in succession by thesuccessive half cycles of the signal wave until the tube associated withthe chosen selecting lead is iired. The firing of this tube applies avoltage to the recycling circuit, which causes a tube to be energizedthat quenches the oscillator and further causes the line coupling tubeto be so conditioned as to prevent the transmission thereafter of anyfurther halfy cycles over the line. Thus at the proper which, under thecontrol of the aforementioned 56 instant, the transmission of the linesignal over the line LN terminates at the end of the proper half cycle.It an even number of half cycles have been generated by the oscillatorOC, the same will stop almost instantaneously. n the other hand, if anodd number of half cycles have been produced. the oscillator willcontinue operating to produce the succeeding even half cycle since thecurrent inthe elements of the oscillator is then owing in thenon-conductive direction of the oscillator stop tube. This half cycle,however, is prevented from being applied to the line by the line clamptube D.

After a .short delay, one of the tubes of the recycling circuit res,causing the tubes of the counting chain to be extinguished but stillmaintaining the oscillator stopped and the line coupling tube inthenon-transmitting condition. The circuit is thus returned to its initialcondition, ready for the transmission of the next signal wave.

In the present embodiment of the invention, the transmitter has beenarranged to send a desired digit either singly or continuously. For

` the latter type of operation, the recycling circuit is arranged sothat, as long as a connection is maintained between the common lead anda selecting lead, the signal corresponding to the selection will berepresented with a recycling pause between groups of half cycles ofabout ten milliseconds.

In the receiver, during an interval when no vsignal is being received,all tubes of the 'counting chain C'IRi-CTRU are maintained in thenonconducting condition. When a signal is received, the ilrst halfcycle, which is positive, causes an essentially square negative Wave,produced in the anode circuit of the first detector, to produce apositive square wave in the anode circuit of the inverter associatedwith this detector. This charges a condenser associated with therecycling circuit, the latter then acting to apply energizing potentialto anodes of the tubes in the counting chain. Near the end of the firsthalf cycle of the signal train, the first detector cuts oi, causing theassociated inverter and impulse ampliiier to apply a positive voltageimpulse to the odd tube/s of the counting chain. The iirst tube of thischain being the only one normally primed, res, priming the first markingtubek and the second counting tube. Near the end of the vsecond halfcycle, the second detector cuts oil', ap-

plying a positive square wave to the recycling circuit.` The condenserof this circuit is arranged so as to discharge with comparative slownessand hence to prevent the recycling function from occurring during theinterval between the termination of the positive square wave produced bythe i'lrst detectors inverter and the beginning of the one produced bythe second detector. Near the end of the second half cycle, current flowis initiated in the anode circuit of the second detector, causing theassociated impulse amplier to apply a positive voltage impulse to theeven number counting tubes. Since the second tube of this chain is nowprimed by the conducting condition of the first tube, it fires, primingthe third counting tube and the second marking tube and removing thepriming condition from the first marking tube. In a like manner thecounting tubes re in turn, each priming the corresponding marking tubeand the following counting tube and removing the priming'condition fromthe preceding marking tube. When the last half cycle of the signal traini received, the positive square waves are no longer n 4 applied to therecycling circuit by the first detectors inverter and the seconddetector. The recycling circuit condenser discharges, causing therecycling circuit to apply a positive impulse to all marking tubes andimmediately thereafter to extinguish all counting tubes. Since at thistime the only primed marking tube is that corresponding to the lastfired counting tube, it is red by the impulse and acts to extinguish anyother,

.the main gap of recycling tube GI is thereby applied between the anodeand cathode thereof, positive potential from positive battery +V beingapplied through-the contacts of key K and resistor RI to the anodeoftube Gl, and negative potential being applied to the cathode of saidtube through the voltage divider composed of grounded resistor RI3 andserial resistors R1 and R6 connected, in parallelwith resistor RIB, tobattery -V. The difference of potential'thus applied between the cathodeand anode of tube GI is sufiicient to .cause the ionization of its maingap and the same is thereby rendered conducting t-o draw currenttherethrough over the abovetraced circuit, whereupon ecrtain specificpotentials are made available at the terminals of various electrodes,terminals and conductors connected with the circuit as indicated below:

The current flowing through the cathodeanode circuit of tube GI causes apotential to be available at the left terminal of resistor R6 which isapplied by direct connection to the grid of the upper triode of vacuumtube B.y The ohmic value of resistor R6 is so computed that thepotential applied to this grid will be such that the resu1ttube, topositive battery +V through resistor R8 and, in parallel therewith,resistor R15 to ground,l

The potential available at the junction point of resistors R15, R8 andR9 consequent to this iiow of current is suiiiicently less positive thanthe full potential of the battery +V as to be a little above thecut-oli" point of tube C. Since the cathode of the tube C is connectedto allof the anodes of the gas-iilled tubes CTI-CTI) and since thecathode's of the latter have a negative potential applied thereto fromnegative battery -V through an undesignated resistance individual toeach of the cathodes, the trickle of an infinitesiv cathode of tubewhich potential, however, is less than required to s tain conductivity.However, since at this time all these tubes are inactive ampere or twois iiowing through them as above set forth, the application of less thansustaining positive potential to the anodes thereof by the C will haveno effect.

The current through the anode-cathode circuit of tube GI is alsoeffective in producing another less negative potential which appears atthe right terminal oi resistor R6 and is applied, through resistor R2Ito the-grid of the lower triode of tube B. Since negative batterythrough resistor R22, with resistor R90 shunted to ground is connectedto the cathode of this lower triode, and the anode thereof is connectedto the upper termina-l of the oscillator coil OC (the lower plate ofcondenser OCN and the lower terminal of the coil OC both being connectedto ground), current will flow through this lower triode to groundthrough the coil OC. The small potential developed at the upper terminalof the coil OC in consequence of this current now holds the condenserOCN charged to the value thereof. Inasmuch as the current thus flowingis a direct current, oscillation of the energy stored in the condenserOCN and the coil OC is thus prevented so long as the current continuesto flow through even though a microthe Ilower triode of tube B. Underthese condiwill be produced for'transmission over the line LN.

It will be observed that the upper grid of the line clamp vacuum tube Dis connected to the common terminal of resistors RI2, RIE and RI1 andthat the lower grid is connected to the common terminal of resistorsRII, RM and Rl8. Resistors RI4 battery +V via the contacts of key K;resistors RI'I and RIB are connected, over conductor I, to the lowermoving contact of each of the numerical keys 1-0 of the key-set KS andto a voltage divider comprising resistors R20 and R5 bridged betweenbattery --V to ground; while resistors RII andvRIZ are connected to thecathe ode of tubeGI. Now resistors RII, RI2, RIA, RI5, RH, RI8 andresistors R20 and R5 (the latter two resistors comprising a voltagedivider) are computed to such values that when tube GI is renderedconducting, the grids of both triodes of tube D are rendered relativelypositive, and if signal voltages be applied current will ow' throughboth triodes effectively to short-circuit the line LN as subsequentlyset forth.

It will further be noted which the signals are to be transmitted isconnected to the cathode of the line amplifier tube L and, also, to theleft terminal ofthe low retions n0 oscillations sistance resistor R23which has its right terminal connected to ground.` Resistors R24-R28form a network which interconnects the grid of the line ampliiier tube Land the mid-terminal of oscillating coil OC, and the object of thisnetwork is to couple the oscillator coil OC with the line LN and withmeans to stop instantly the transmission of signals over the line LNthrough the control exercisedv by both triodes of tube D. It will alsobe observed that the anode of the upper triode of tube D is connected toground and that the cathode is connected to the aforementionedresistance networkat the junction of resistors R26 and R21,",whereas theanode of the lower triode is connected to the network at the junction ofresistors R25 and R26 while the cathode is connected to ground.. -Sinceeach triode or the vacuum tube D conducts in one dithat the line LN overand RIS are connected to positive tial when tube GI is conducting, itfollows thatk one triode of tube D acts as a low resistance cir- Acuitbetween the network and ground for, curl rents generated in thedirection ci its conductivity and the other triode is a low resistancecir- Cuit between the network and ground for currents generated in thedirection of its own conductivity, thus preventing tube L fromtransmitting signals over the line. In other words, as long as key Kalone is operated and none of the numerical keys 1,0 oi key-set KS isoperated, the condition of the transmitter is such that the oscillatorcoil OC is blocked, less than sustaining potential is applied to theanodes of the tubes CTI-CTO ci the counting chain and a high attenuationis established across the line LN by the triodes of tube D to preventcurrents in either direction from getting through.

The present embodiment of the invention is arranged either for therepetitive transmission of the same digit or for the single transmissionof one digit only, the digit transmitted in either case being controlledby Whichever numerical key of the key-set KS is depressed, key S2, inits operated position. controlling the transmission of a single train ofimpulses and in its normal position controlling the repetitivetransmission of the same train of pulses indicated by the operatednumerical key. Assume, therefore, that a single signal train of pulsescorresponding to a "5 selection is lto be transmitted. With key S2operated, the numerical key 5 of key-set KS is then operated. With keyS2 operated, resistor R35 which is connected to the anode of the tube G2and to the left plate of condenser C3 is grounded, and since current forthe circuit oi tube G2 is drawn from battery +V through resistor R2, thegrounding of resistor R35 causes it to be connected in shunt withresistor R2 so that .the potential available at the anode o'f tube G2for applying a charge to the left 4plate of condenser C3 is less thanthat available through the anode of tube GI forchargingthe right plateof said condenser. 5 connects, through its lower contacts, the cathodeof counting tube CT5 to conductor I, while through its upper contacts itcompletes a charging circuit for condenser C2 of large capacity andcondenser CI of relatively smaller capacity, the charging circuit ofcondenser C2 extending from positive battery +V, contacts ofvkey K,resistor R30, upper contacts of key 5, condenser C2 to ground. Thecharging circuit for condenser CI extends from battery +V throughcontacts of key K, resistor R30, upper contacts of key 5,

left operated contacts of key S2, condenser CI. resistor R3I to thepotentiometer arm of resistor R32 (which is one of the resistanceelements of the potentiometer network extending from battery -V toground via resistors R3, R32, R33, right-hand inner operated contacts ofkey S2 to ground). The impulse thus created in the condenser CI raisesthe potential of the control anode of tube G2 sufficiently to causeionization of the critical gap thereof, inasmuch as the cathode isconnected to lnegative battery -V. This ionization spreads to the maingap since positive battery from source +V is applied to the anode of thetube via resistor R2 and the' The operation of key A the tube Gi causesthe assensoY y upper contacts of key`fclose before its lower This, ofcourse, could be obviated by a of the key contacts.

There is, moreover, a relatively large capacity CS connected between theanode of tube Gi and that oi tube G2. During the conductivity4 of tubeGl, the right plate of this condenser acquires a charge, of course,which depends upon the potential available at the anode of the tube Gl.When tube G2 lres, a parallel path to resistor R35 is establishedthrough tube G2 thus lowering the potential at the anode of tube G2. Thelowering of the potential on the left-hand platev of condenser C3(connected to the anode oi' tube G2) causes condenser CS to begin tocharge and since the charging current is drawn through resistor Rl, theanode of tube Gl is momentarily made much less positive and thelattertube is extinguished. A negative source of voltage is furnished tothe cathode of tube Gi via its connection '4to the junction of resistorsRS, RIE and Ri, which resistors form part of a potentiometer circuitextending from negative battery V, .via the combination of resistors RISin parallel withl serially-connected resistors Rl and R6, and thence viaresistor R43 to ground. The extinguishing of tube GI causes the ow ofplate current in this potentiometer circuit to cease, and the potentialof the cathode, and of lead 2 connected thereto, to become morenegative. 'I'he grids of both triodes of tube D, by virtue of theirconnection to lead 2 vla resistors contacts. sequence adjustment A RHand Rl2, assume a negative polarity, said grids now eiectivelypreventing any current from owing through their associated anode-cathodecircuits so that any energy which is thereafter produced by theoscillator is applied to the amplifying tube L instead of beingshort-circuited to ground through the triodes of tube D. 'I'he signalapplied to the grid of tube L will thereafter partly be carried toground over resistor R23 and partly applied over the line conductor LNto the receiver.

The extinguishing of tube GI further causes the potential at thejunction of resistors R1 and R6 to become more negative, and thispotential is applied to the grid of the upper triode of tube B.' In asimilar manner the extinguishing .of

potential at the junction of resistors R2I and R34 to become morenegative and this potential is applied to the grid oi' the lower triodeof tube B. The lower triode 0f tube. supply the oscillator coil OC withdirect current duringthe times thatthe grid of said lower triode ispositive; that is, during the time when tube GI is conducting. Hence,when tube GI is extinguished and the lower grid of tube B is madenegative as an indirect result of theconductivity of tube G2,thiscurrent is suppressed and the energy stored inthe oscillator coil OCand condenser OCN begins to oscillate to produce a continuous train ofalternating current waves as set forth in the above-mentioned patent,the lower triode of tube A functioning to supply the required energy toproduce sustained oscillations. Since the anode ofthe lower triode oftube B is connected to the common terminal of oscillator coil OC andcondenser OCN, the ilrst half cycle of the current will be positive.

It will be remembered that during the conductivity of tube GI thecurrent flowing in the 1S IeInOVed.

B, it will be remembered, operates to y C is made more cathode-anodecircuit ,thereof caused the grid ot the upper triode of tube B to bemaintained at a positive potential so that this triode would conduct andthat, in consequence, a relatively negative potential was applied to thegrid of tube C which established an inappreciable current through theanode-cathode circuit thereof. including the anode-cathodepath of eachgaslled tube in the counting chain GTi-CTU. Now When tube Gl isextinguished, cessation of the anode-cathode current through the uppertriode of tube B causes the anode to become more positive in consequenceoi' which the grid oil-tube positive. The greater current nowowing'through anode-cathode 'circuit of tube C raises the availablepotential at the anode of each oi' the counting tubes CTl-C'Iii to avalue such that, when one oi them is rendered conducting through itscontrol gap as 4hereinafter set forth, the voltage available at theanode of that tube from the cathode ci' tube vC will cause said tube inthe counting chain to become conn ducting throughvitsmain gap, thuscausing it to remain operated when the initial breakdown' voltagebetween its cathode and control anode yescalator is picked ou theoscillator coil OCand ap- R2B whence, through re- The output of themid-terminal of the plied to the resistor sistor R29, part of it andwhence, through a voltage divider composed of Yresistors R27, R26, R25and a portion of the, resistor Rit, a part of it is applied to the gridof the` line amplifying tube L, whereby the anode-cathode current inthis tube is caused to :be modulated in accordance with the character ofthe oscillating voltage applied to the grid thereof which, in turn, isproportional to, and in accordance with, the character 'of the voltageproduced by the oscillator coil OC. The anodecathode oscillating currentin the line tube L passes through resistor R23 which is connectedbetween the cathode of the tube and ground, and the voltage dropdeveloped across this resistor is applied to the line conductor LN fortransmission thereover to the receiver which, as set forth hereinafter,responds'to the oscillations and provides a suitable indication thereof.It should be` noted at this point that if the grids of both triodes oftube D werenot rendered negative when tube Gl is extinguished, theoscillating energy, instead of being applied to the line LN as abovenoted, will pass to ground, the positive half cycles of the energypassing through one triode of. tube D and the negative half cyclespassing through theother triode of tube D. 'I'he fact that the grids ofthis'tube are rendered negative at the time tube Gl vis extinguishedcauses the triodes of this tube to present practically an open circuitto the potentiometer network between the oscillator and the grid of theline tube L so that the oscillations are reproduced in tube L .andpassed into the line conductor LN,

The upper triode of tube A together with transformer IT form an The gridof this triode is connected serially through the high resistanceresistor R16 to the common terminal of the oscillating coil OC andcondenser OCN", and the alternating voltages prof duced by theoscillator correspondingly alter the .potential of said grid. Thesevoltages, however, are so large that they drive the grid from the pointof cut-olf to a positive value, a fact which, coupled with theadditional fact of the high resistance of resistor R18, causes ananode-cathode is drained oil to ground impulse producing device.`

Awhich supplies the bias.

9 current flowing through the upper triode of tube A to be essentially asquare top wave. Now the first half cycle produced by the oscillator ispositive and during this period current will ilow in the upper triode oftube A through a circuit which traces from positive battery -1-V`throughresistor R9I, the two left, or primary, windings of transformer IT,through the anode-cathode path, to ground on the cathode. At the end ofthe rst half cycle, the grid of the upper triode of tube A becomesnegative with respect to its cathode, and anode current, therefore,ceases to ow through the primary of transformer IT. The cessation ofcurrent is'very abrupt due to the square-top character of the wave, anda sharp impulse is thereby caused to be generated in the secondarywinding of transformer IT, which appears as a positive impulse atterminal 2 connecting with the control anodes of the odd numbered tubesCTI-CTB, and as a negative impulse at terminal I` which is connected tothel control anodes of the even numbered tubes CTZ-CTO. The controlanode of tube CTI, however, is at ground potential. Since the cathodesof all the counting tubes CTI-CTU are connected to negative battery -Vthrough appropriate resistances, the application of the positive impulseto the control anode of tube CTI via its associated undesignatedcondenser raises the potential of said control anode to a value whichestablishes a control gap breakdown difference of potential between itand the negative potential available at the cathode, causing the controlgap to ionize. Since an appropriate positive potential is, at this time,also4 applied to the anodes of all counting tubes from the cathode oftube C, as previously explained, ionization of tube CTI spreads to themain gap, in consequence of which the tube will remain in a conductingstate upon the termination of the impulse, the current flow path throughthe main gap of tube CTI tracing from positive battery +V through theanode -cathodev path of tube C,

anode-cathode path through'the tube CTI, and

the undesignated cathode resistance to negative battery -V. The ow ofcurrent through the 'cathode resistor of tube CTI produces a relativelypositive potential at the cathode which is applied to the control anodeof the next tube CTZ through an interconnecting resistor. Thispotential, however, is not suiicient to cause the breakdown of thecontrol gap of tube CTZ, said potential serving only to bias the controlanode of this tube for breakdown purposes upon the application theretoof an additional potential over that The other odd numbered tubes towhose control anodes the positive impulse from transformer IT is appliedat the time it is applied to the control anode of tube CTI are not redwith tube CTI because, while the control anode of tube CTI is normallyat ground potential, the control anodes of the other odd numbered tubesare Amaintained at a voltage more negative than ground by means of theresistance network interconnecting -V and ground.

At the end of the second half cycle, current flow is again initiated inthe plate circuit of the upper triode of tube A, the change in currentbeing effective to produce an impulse in the primary windings oftransformer IT which is opposite in polarity to that produced at the endof the rst half cycle and, consequently, causing a positive impulse toappear at the No. 1 terminal of the secondary windings of transformer ITand a negative impulse at the No. 2 terminal.

relatively positively biased by the cathode potential derived from theconductivity of tube CTI,

the positive impulse now applied to the control anode of tube CTZ willcause it to re, in turn conditioning the control anode of tube GT3 to beresponsive to the next'positive impulse to be applied thereto from theNo. 2 terminal of transformer IT.V A series combination of v aristor VRand resistor R36 shunted across the two primary windings of transformer1T serves to equalize the amplitude of the impulses produced at the endsof the odd and even half cycles, which amplitudes would otherwise beunequal because the inductance of the primary winding causes its currentto rise more gradually at the ends of even half-cycles than it decays atthe ends of odd halfcycles.

In the above manner, counting tubes CTI-CTS fire, each in turnconditioning the succeeding tube. When, at the end of two and a halfcycles, tube CT5 fires, the flow of current between its anode andcathode renders said cathode relatively positive. Since the cathode ofthis tube is connected to conductornl through the lower contacts of thenumeral key 5, and the conductor is, in turn, connected to the grid ofthe lower triode of tube B via resistor R34 and to the grids of bothtriodes of tube D via resistors RII and RIB, all of said grids arerendered positive. As a result the anode-cathode impedance of bothtriodes ofr tube D is reduced to a fairly low value, the signal from theoscillator is greatly attenuatedacross the potentiometer resistor R24,and tube L is prevented, after the transmission of two and one-halfcycles, from applying any further signal energy whatsoever to the lineconductor LN. v

Due to the fact that, at the end of the two and one-half cycles, currentin the oscillator OC is flowing toward ground and since the upperterminal of the oscillator is connected to the lower anode of tube B,the triode of which this anode is a part will fail to conduct eventhough its grid is positive with `respect to its cathode. The oscillatorOC, therefore, fails to stop until, at some time later near the end ofthe third cycle, the current reverses, the anode of the lower triode oftube B becomes more positive than the cathode and current again ilowsthrough this triode to thereby return the oscillator to its vsteadystate stopped condition as originally described. This,

however, will in no way aiect the line since, as

before stated, the conductivity of the two triodes of vtube D preventssuch voltage from being impressed on the grid of tube L even though theoscillator 0C is still functioning.

The positive potential upon conductor I is also applied to the controlanode of tube GI through resi-Stor R31. After a delay due to the timerequired to charge condenser C4, tube GI fires across its control gapand thence across its main gap to cause its anode potential to becomemore negative and its cathode potential to become more positive. Due tothe connection of condenser C3 between the anode of tube GI and that oftube G2 and due to the fact that thisy condenser is charged to thevoltage of the drop across resistor R2, the fact that the anode of tubeGI is rendered more negative by its conductivity causes is made morepositive than it was before, and this positive potential is, of course;applied to the grid of the upper triode of tube B to cause current toflow through its anode-cathode circuit. The anode being rendered morenegative by the current flow, the relatively negative voltage thereof isapplied to the grid of tube C in consequence of which the currentthrough the anode-cathode is reduced and the potential of the cathodebecomes su'lciently negative so that the voltageA applied to the anodesof the counting tubes is insuflicient tomaintain a discharge. T ubes CTIto CTB therefore become extinguished.

The extinguishment of tube CTB causes conductor I to become morenegative, but the effect of this on the grids of tube D and that of thelower triode of tube B is compensated for by the fact that the cathodeof tube GI has become positive by an equal amount. The reason for thisis because the more positive potential at the cathode of tube GI isapplied to the lower grid of tube B via resistor R2I at the same timethat conductor I supplies a less positive voltage to the same grid viaresistor R34. In the same manner, the more positive potential on thecathode of tube GI is applied to the two grids of tube D via resistorsRIZ and RII at that same time that conductor I supplies a less positivevoltage to these grids via resistors RI1 and RI8. Since the firing oftube GI and the extinguishing of tube CTS occur practicallysimultaneously, the grids oi `the above triodes remain at asubstantially constant potenf tial. The circuit is thus returned to itsinitial condition except for the fact that, since numerical key 5 isclosed, condensers CI and C2 remain charged over previously describedpaths and, therefore, no impulse will be produced across condenser CI toilre tube G2. To produce the impulse, numerical key 5 is released andkey 5 or some other numerical key reoperated. Upon release, condensersC2 and CI are discharged and, upon reoperation, condenser C2 will becharged and later condenser CI' will be charged as previously described,producing an impulse that will cause tube G2 to fire and the operationsabove s described to be repeated.

Other signals may be sent in the same manner as above described exceptthat in the case of even numbered signals the oscillator stopsimmediately 'at the end of the last half-cycle of the signal since thedirection of current ow at this time is in the conductive direction ofthe lower triode of tube B and the voltage applied to the plate of thistriode is more positive than that of the cathode.

For the continuous transmission of the same signal only the numericalkey correspondng to the number of the signal to be transmitted isoperated, key S2 being kept in its unoperated condition. At the end ofeach signal train when tube GI has red and extinguished tube G2, thelatter tube retires across its control gap after a delay which may becontrolled by the adjustment of the potentiometer R32. Ihe reason forthis is that when tube GI extinguishes tube G2, the anode potential ofthe latter becomes morepositive with respect to the potential suppliedby battery -V at the cathode. However, due to the fact that key S2 isnormal, the control anode is tied to the main anode via resistors R3 I,R32 and R33. Hence the potential of the control anode similarly becomesmore positive with respect to the potential available at the cathode.Both these potentials, however, are derived from the charging circuit ofcondenser C3 which includes battery -V, resistors R3, R32. and R33,right inner normal contacts of key S2, condenser C3, resistor RI,contact of key K to positive battery +V; in parallel therewith there isalso the potential available at the lower terminal of resistor RI due tothe conductivity of tube GI, and also the parallel resistor R2 tobattery +V through the contacts of key K. The potential applied to thecontrol anode of tube GI, being derived from the above network and beinga. function of time, can be derived for any particular time value bysuitably adjusting the potentiometer R32. When the appropriate value ofpotential is reached, tube G2 will tlreacross its control gap and theoperations above described will be repeated. Thus, without any furtheroperation of keys, repetitive signals will be transmitted.

The delay feature in the flringand extinguishing of tubes GI and G2 andthe correspondingly necessary joint control of the recycling operationsby the potentials on conductor I an-d at the cathode of tube GI arenecessary in order to obtain a short recycling time in continuoussending. In the transmission of a "1 signal, vfor example, the durationof the signal may be 2 milliseconds. If tube GI were to be firedimmediately by the positive potential on conductor I, it could remainextinguished for only 2 milliseconds whereas the deionization of a tubeof this type requires at least 5 milliseconds and the value of condenserC3 is such as to delay the rise of plate potential suillciently t0permit such time for deionization. However, with a 4-mi1lisecond delayin the firing .0f tube GI (which can be arranged by the proper choice ofvalues for .condenser C4 and resistor R31), it can remain extinguishedfor 6 milliseconds in the transmission of a 1 signal. Thus the circuitis so arrangedythat during continuous transmission of this shortestAsignal combination, and with a recycling time of 10 milliseconds, tubesGI and G2 commutate at approximately equal intervals.

The operation of the receiver will now be described. It is assumed thatfilament current for the vacuum tubes .of the receiver ows through thefilaments thereof from any suitable source of current (not shown) andthat, in consequence, the respective cathodes of the tubes are in anemitting condition. In the no-signal condition, no current ow throughthe upper triode of detector tube DETI since the grid thereof ismaintained at a cut-oir negative potential which is derived from avoltage divider comprising resistors R40 connected to negative battery-V through conductor 5, REI and R45, the latter being connected to apositive source of potential -l-V over conductor 2. The ohmic values ofresistors RSI and R40 are computed to a value that will permit nocurrent ow through the anode-cathode circuit of the upper triode of tubeDETI. On the other hand, current is flowing through the anodecathodecircuit of the upper triode of detector tube DET2 because the potentialat the grid thereof isavailable from the voltage divider comprisingresistors R4I connected to negative battery -V over conductor 5, andresistors R44 and R45, the latter being connected to positive bat-y teryas above mentioned. The ohmic value of resistors R44 and R4IV iscomputed to a value that will permit current now through theanode-cathof this voltage divider are computed so that the normalpotential on said grid permits current to ow through the upperanode-cathodeof said tube INV, the path of said circuit tracing frompositive battery +V, conductor 2, resistor R64, through the upperanode-cathode path of tube INV to cathode' ground. Thus current flows inthe anode-cathode circuits of the upper triodes of tube DETZ and theinverter tube INV and the potentials on the anodes of the upper triodesof both tubes are applied through resistors R41 and R50 respectively tothe plate and grid of the lower triode of tube RE. Resistor R48 isconnected to and through RI to condenser A and to battery +V overconductor 5 so that, with the positive potentials on the. anodes of theupper triodes of tubes DETZ and INV obtaining at this time', thepotential at the, junction point is negative with respect to ground andcauses condenser A to be charged negatively through resistor R5I.- Thenegative potential on condenser A is applied to the grid of the uppertriode of the recycling tube RE via resistor R52, thereby causing nocurrent to now through the anode-cathode circuit thereof.

. which, through resistor R55, is applied to the grid since the grid ofthe iower triode of the inverter l tube INV is connected to the upperanode of tube RE through resistor R82, the potential on this grid, asmodified by the connection of said grid to negative battery -V viaresistor R81 is, therefore, positive with respect to its cathode. Thispermits current to llow through the anode-cathode of the lower triode oftube INV, and the potential on the anode of this triode, which isrelatively negativel'due to the ow of plate current from positivebattery through resistor R19 is transmitted to the grid of theextinguishing tube EXT through resistors R54 and R53. The value of thispotential causes only a very slight current ow through the anode-cathodeof tube EXT and the anode-cathodes of each of the gas-lled tubes of thecounting chain C'I'RI-CTRB to negative battery -V, which maintains thecathode potential of tube EXT sufficiently negative that the voltageapplied to the anodes of the tubes CTRI-CTRD of the counting chain isinsufficient' to maintain a discharge through any of these lastmentionedtubes.

In the rio-signal condition upon line LN, the

of the lower triode, causing a further amplified change in voltage toappear inthe anode of said lower triode.

'Ihe first half cycle of the incoming signal, which is positive, isapplied to the grid of the upper triode of tube RL, causing thepotential thereof to be rendered less negative. More current now flowsthrough the anode-cathode circuit of the upper triode of this tube, andthe potential developed across resistor R55 as a result of the increasein current renders the grid of the lower triode more negative thanpreviously, and thereby increases the potential of the lower anode. Forsmall Values of signal voltage this increase in potential is a'two-stageamplication of the potential of the rst half cycle of the incomingsignal. For larger values of signal voltage the peak of the half-cyclemay be flattened las the grid of the lower triode attains a potentialwhich causes the cessation of current in the anode-cathode path, butthis will not adversely aiiect the action of the receiver.

The potentials across the voltage divider comprising resistors RSI andR40 and across the voltage divider comprisingresistors R44 and R4! whichresult from the amplication of the signal are applied, respectively, tothe upper grids of detector tubes DETI and DET2. Since the rst receivedsignal is positive, these grids become more positive and, at some valueof signal which exceeds the noise level on the line circuit LN, currentflows through the anode-cathode circuit of the upper triode of detectortube DETI. The current iiow in said triode causes the potential of itsanode to become more negative, 4and this more negative potential isapplied, via resistor R46, to the grid of the upper triode of invertertube INV. The anode potential of this triode now becomes more positive,but this has little effect on the grid of the lower triode of tube DETIto which it is connectedby way of condenser B since its grid is alreadypositive with respect to its cathode due to the potential available onsaid positive battery +V on conductor 2.

grid of the upper triode of the line receiving tube RL is maintained ata slightly negative potential through resistor R58, variable resistorR59 and resistor R60 which is connected to negative battery -V. Underthis condition, some current flows through the upper triode, path whichextends from positive battery +V, resistor R51, anode-cathode path tocathode resistance ground. The anode of the upper triode of tube RL is,therefore, at a potential less positive than the full positive batterypotential, and this potential, as modied by potentiometer comprisingresistors R andv R56 to negative battery V, is connected to the grid ofthe lower triode of this tube, thereby maintaining said grid at apotential which will cause some current to ow through the' grid as aconsequence of its connection to the common terminal of resistors R63and R62. Since little or`no current is flowing through the upper triodeof tube INV, the anode thereof is relatively positive by virtue of thesmall voltage drop in resistor R64 which interconnects said anode andHence, while this anode is relatively positive during the time that nocurrent ows through the associated anode-cathode circuit, this positivepotential is also available at the anode of the lower triode of therecycling tube RE, which is used as a diode, so that current ilowsthrough the anode-cathode circuit and a positive charge is applied tocondenser A. Since the plate of this condenser is connected to the gridof the upper triode of the recycling tube RE via resistor R52, saidupper grid likewise acquires a positive potential the effectv of whichis to cause the associated upper anode I of this tube to become morenegative, carrying with it the grid of the lower triode of tube INV.This causes the potential at the anode of the latter triode of tube INVto become more positive, carrying the grid of tube-EXT towards positivealso. Thus, the cathode of tube EXT is permitted to become suicientlypositive to apply to the anodes of the counting tubes CTRl-CTRO ananode-to-cathode potential greater than their sustaining potentials. l

The change toward positive of the anode of the lower triode of tube INVapplies a positive im- 15 pulse through condenser D to the grid oftriode SEL. Since said grid already has a positive potential applied toit from resistors RI00, RIOS and RI03, the anode-cathode current islittle afl fected and hence the anode potential remains substantiallyconstant. It should be remembered that during the reception ofthe firsthalf-cycle of signal, positive potential was not only applied to thegrid of the upper triode of tube DETI as already explained, but also tothe grid of the upper triode of tube DET2. Since this merely constitutedan increase of the existing positive potential applied through resistorR42 to said grid, and

-in consequence of the large value of resistor R42,

only a small increase in grid current results, and there is practicallyno change in the anode-cathode current in the upper triode of vtubeDET2. The anode potential therefore remains substantially constant.

.Near the end of the first half cyc1e of the smus- 20 oidal half waveproduced by the transmitter, the grid of the upper triode of tube DETIbecomes negative with respect to the cathode, the signal being appliedto the gridl of thisupper triode through the two-stage ampliercomprising both triodes of tube RL. The anode potential on the anode ofthe upper triode of tube DETI, therefore, increases in a positivevdirection which, in

nitude of this impulse is insuiiicient to re the control gaps of thesetubes, but since the control anode of tube CTRI is provided with apositive bias relative to its cathode through resistors RSS,

e R61 connected to ground and resistor R66 in parallel thereto connectedto negative battery -V, tube CTRI ilres across its control gap to thenegative potential at the cathode supplied from battery -V through anundesignated resistor. The tube then fires across its main gap to thepositive potential supplied by the cathode of tube EXT and remains in aconductive state until this potential is removed or reversed.

When tube vC'IRI ilres, the current drawn through its anode-cathodecircuit causes the cathode potential to become more positive, car'-rying with it, in the positive direction, the control anodes of tubesCTR2 and SI, the latter tube being the rst tube in the marking chain.The potential for the control anode of tube CTRZ is applied throughresistor R69 while that for the control anode of tube SI is appliedthrough resistor R10. The applied potentials are, however, insufficientto re either of these two tubes be'- cause, in the case of tube CTR2,the diiference in potential between thecontrol anode and the cathodewill not reach the breakdown value until a positive impulse is appliedto its control anode by way of condenser CN 2 Since the positive im-vpulse which red tube C'I'RI. is also applied to control anodes of allthe odd-numbered tubes but not to the control anodes of theeven-numbered ones, tube CTR2 cannot be fired on the same impulse whichred CTRI. In the case of tube SI, the potential applied to its controlanode is insulclent to ilre said gap in the absence of large positivepotential at the plate of tube SEL.

Soon after the beginning of the second halfcycle of the signal train,which second lhalf-cycle triode of tube INV, said potential beingapplied v through resistor R50 and the lower diode of tube RE. In otherWords, during the reception of a train of positive and negativehalf-cycles, condenser A is continually charged'. Now resistor RSI,which is virtually short-circuited during the charging of condenser A,appears in the discharge circuit of this condenser, which dischargecircuit terminates at' the potential available at the common terminal ofresistors R48, R50 and R41. The ohmic resistance of resistor RSI and thecapacity of condenser A are so computed that the time constant ondischarge is long enough to prevent appreciable discharge of thecondenser during the short instants between the latter part of eachhalf-cycle and the early part oi. the following half-cycle and,therefore, the potential on the grid of the upper triode of said tube RE(via resistor R52) is prevented from becoming negative.

Near the end of the second half-cycle, the grid of the upper triode oftube DET2 becomes positive with respect to the cathode. The anodepotential now becomes more negative, applying a negative impulse throughcondenser C, tothe 40 grid of the lower triode of this tube. Theresulting positive impuls'e on the anode of this lower triode isapplied, through condensers CN2, CN4,

CNS, CNB and CNO to the control anodes of the even-numbered tubes CTR2,CTRA, CTRG, CTR8 and CTRO. Unaided, the magnitude of this impulse isinsufilcient to fire the control gaps' of these tubes. Since, however,the current in the cathode circuit of. tube CTRI has caused a positivebias to be applied to the control anode of` the ilow of current in thecathode resistor of.

tube CTRI. In this way, the tubesCTR of the counting chain are fired insuccession, each in turn biasing the control anode of the correspondingmarking tube and the succeeding countingr tube, and neutralizinguthebias of the preceding marking tube. It--will now be `shown that, inM

response to operatio'rs following the reception of a last pulse or'vhalfcycle in a signal train, the

" marking tube orresponding to the last fired counting tube will also-be fired and remain in the conducting state, thus indicating by itsnumerical designation the number of half cycles received. This tuberemains in a fired condition until the last half cycle of a succeedingsignal train is received, at which time the marking tube previously redis extinguished and the marking casacca tube indicative of the lastpulse in the second signal train is fired, Obviously, il both signaltrains contain the same number of half cycles, the same marking tubewill remain lighted.

Suppose, for example, Vthat signal is being received and that a previoussignal train of three half cycles (3), having been received, will havecaused marking tube S3 to have become fired and to have remain lightedin the manner shortly to be explained. After the end of the fifth halfcycle, no further signals will be' received. Condenser A will thendischarge through resistor RSI to the point where the grid of the uppertriode of the recycling tube RE becomes negative with respect to itscathode. The fiow oianode current in this triode will thus beinterrupted and the anode potential will become more positive, carryingwith it the grid of the lower triode of tube INV. The anode potential ofthis latter triode now becomes more negativeapplying a negative impulsethrough condenser D, to the grid of tube SEL. The resulting positiveplate Apotential of tube SEL causes a positive impulse to be appliedthrough conductor 6 and condensers SNI-SND to the control anodes ofmarking tubes Sl-Sll', firing tube S5 since it is the only one of themarking tubes which is primed at this time.

In connection with tube S3, assumed to be previously conducting, thepotential of its cathode is maintained at a constant positive value bythe charge in condenser CC3 accumulated The more negative potential onthe anode of the lower triode of tube INV is applied to the grid o! tubeEXT by way of resistors R54 and R53, from whose junction point acondenser E is bridged to ground. Said condenser dela-ys the change o!potential at the grid of tube EXTl sufliciently long to permit theabove-described action of tube SEL to take place. Thereafter, thenegative potential on the grid of the tube EXT causes the cathodethereof to become more negative. The potential appliedthereby to theanodes of the counting tubes CTRI-CTRU is now no longer sufllcient tosustain a discharge. Hence, counting tubes CTRl-CTR5 extinguish. Themarking tube S5, however, remains lighted. Otherwise the circuit isreturned to its initial conidltion, ready for the receipt of the nextsignal tra n.

While we have described our invention in connection with its applicationto a specic signal transmitting and receiving arrangement, it is thereonby the voltage drop across the cathode resistor. It will also be notedthat the anode current for any of the marking tubes is drawn through theresistor RBI, and the drop across.

this resistor, with one markingtube conducting, will still providesuflicient anode potential so that the diierence between said anodepotential and the potential maintained at the cathode of a conductingmarking tube, like tube S3 by its associated charged condenser C63,.will be suilicient to keep the tubein a conducting condition.

Now when tube S5 is fired subsequent to the reception of the fifth (andlast) half-cycle of the second signal train, the current throughresistor RBI is increased since current now flows through'both tubes S3and S5. As a consequence,

the voltage across resistor RBI is also increased.

and the voltage available at the anode of the marking tubes is reduced acorresponding amount. Since condenser OC3 is charged to a positivepotential and condenser CC5 is uncharged at the time tube S5 is iired,the potential difference Vbetween the cathode and anode of tube S3 isnow reduced below the sustaining valve, in consequence of which tube S3is extinguished. On the other hand, the potential difference between theanode and the cathode of tube S5 is the full dlierence between thepotential on the anode and that of the potential divider connectedbetween the negative battery -V and ground, Aand is suiiicient tomaintain the tube S5 in a coriducting state.

It is now evident that if the second signal train contains the samenumber of half-cycles as the first signal train, said first trainalready having caused the lighting of the appropriate marking tube, thistube remains lighted continuously. Thus, if tube S5 is lighted, thesustaining voltage is undisturbed between the successive signals.Although lthe control anode of tube S5 will be primed in the regularcourse of operations as already described, such priming will, of course,have no effect upon the tube since it is already conducting,

understood that various other applications and embodiments thereof maybe made by .those skilled in the art ywithout departing from the 'spiritof the invention as dened by the scope of the appended claims. Thus, arelay may be included in the anode circuit of each of the marking tubes,which will operate when the tube is rendered conducting, in turnoperating a suitable register circuit that includes steering devices forswitching the relays from one registerto the next, thus registering aseries of numbers indicative of the number of half-cycles in each of thesignal trains received.

It is also apparent that, by doubling the number of counting tubes andmarking only every other pulse, the signal transmitted can berepresented by the number of whole cycles instead of half cycles.

What is claimed is:

1. In a signaling system in combination, a line,

an oscillator connected to said line, electronic means normallyeffective 'to short-circuit said line, and controllable means foroperating said oscillator and said electronic means whereby the formerproduces a predetermined number of half y cycles for application to saidline and the latter will ilow through the anode-cathode path of removesthe short-circuit from said line to cause said predetermined number ofhalf cycles to be transmitted thereover, said controllable means beingthereafter effective to quench said oscillator and to cause saidelectronic means to reestablish the short-circuit of said line toprevent spurious oscillations produced by said oscillator afterquenching frombeing transmitted over said line.

2. In a signaling system in combination, a line, an oscillator adaptedto produce a current wave substantially sinusoidal in character fortransmission over said line, .a potentiometer connected between saidline andsaid oscillator, a rst electronic device having itsanode-cathode path connected at one point of said potentiometer in thedirection of the current ilow of a positive half cycle of said currentwave, a second electronic device having its cathode-anode path connectedatl another point in said potentiometer in the direction of the currentflow of a negative half cycle of said current wave, and means forapplying a positive potential to the control electrodes of both of saidelectronic devices, whereby each half cycle of current generated'by saidoscillator either device, depending upon its direction.

3. In a signaling system in combination, a line, an oscillator adaptedto produce a current wave cycles of said current wave, a secondelectronic device having its cathode-anode path connected at anotherpoint of said potentiometer in the direction of the current flow of thenegative half cycles of said current wave, means for applying a positivepotential to the control electrodes of both of said electronic deviceswhereby each half cycle of current generated by said oscillator williiow through the anode-cathode path of leither device depending upon itsdirection, andmeans -for changing the potential at the controlelectrodes of both of said electronic devices from positive to negative,whereby a high impedance is offered in the anode-.cathode path of saidelectronic devices to the current from said oscillator, and whereby inconsequence of said high impedance said current isv applied to saidline.

4. In an alternating current signaling system the combination with atransmission line of a transmitter connected to said line comprising analternating current oscillator adapted to produce a current wavesubstantially sinusoidal in charcurrent wave and a path of low impedanceto negative half cycles of a current wave, whereby any cycles oi' thecurrent produced by said oscillator will pass through said paths, apluralityy of numerical keys, a plurality or gas-lled tubes arranged asa counting chain, means responsive to operation of one of said numericalkeys for selecting a tube corresponding to the digit of the key forstarting the operation of said oscillator and for operating saidelectric coupling means to change said paths from low impedance to highimpedance whereby the half cycles of the signal acter for transmissionover said line, means for i determining the number of the positive andnegative half cycles of said current to be transmitted over said line,an electronic counting chain responsive to said means for counting saidnumber ofv half cycles, electronic means bridged between said oscillatorand said line for short-circuiting positive and negative half cycles ofsaid current vtransmission of the last half cycle oi.' the signal wavefor reactivating said electronic means, whereby a short-circuit is againapplied between said oscillator andsaid line and for stopping theoperation of said oscillator.

5. In an alternating current signaling system adapted for the repetitivetransmission of signals,

the combination with a transmission line, of an oscillator adapted toproduce a current wave substantially sinusoidal in character fortransmission over said line, va pair of gas-filled tubes ot which one isnormally in a. conducting state, electronic coupling Ameans between saidoscillator and said line responsive to said conductive. gaslled tubefor'applying across said line a path of low impedance to the positivehaii.' cycles or a current pass over said transmission line, a de-.tector circuit responsive to each half cycle of the signal current forproducing an impulse to operate, in succession, the tubes in the chain,means responsive to the operation vof the selected tube for operatingthe other of said` pair of tubes, means responsive to the operation oi.the other of said pair of tubes for stopping said oscillator, foroperating said electronic coupling means to change said paths from highto low impedance whereby the transmission of further half cycles, oversaid transmission line is prevented,v and for quenching the first ofsaid pair of gas-nlled-tubes whereby said means for operating the rst ofsaid pair of gas-lled tubes is again eiective to operate said tube torestart the transmission cycle, and means responsive to the yreoperationof the rst of said pair of gas-nlled tubes for quenching the second ofsaid pair of gas-fille tubes. HENRY M. BASCOM.

ROBERT E. MASSONNEAU. BERNARD OSTENDORF, Ja. WILTON T. REA.

40 ille of this patent:

Number Name Date 2,248,937 Bellamy 1' July 15, 1941 2,192,217 BellamyMar. 5,A 1940 2,225,680 Boswau D ec. 24, 1940 2,096,954 Bellamy Oct.26,1937

2,241,156 Powell May 6, 1941 2,373,134 Massonneau Apr. 10, 1945.`

2,332,300 Cook a O'ct. 19, 1943 1,882,010 Hershey Oct. 11, 19322,273,193 Helsing Feb. 17, 1942 1,930,609 Davidsmeyer Oct. 17, 1933FOREIGN PATENTS Number Country 1 Date 355,705 Great Britain Aug. 24,1941 485,703 Great Britain May 24, 1938 411,903

4UNITED STATES PATENTS Great Britain June 15, 1934

